Typically, an antireflection treatment is applied to a lens, cathode ray, or the image display surface of a liquid crystal display device to reduce the reflection of ambient light such as sunlight or electric light, and to enhance light transmission. For the antireflection treatment, a method for evaporating magnesium fluoride, which is a low refractive index substance, by a vacuum evaporation method, has been widely used. However, in accordance with an increase in the size of displays, a coating method that is excellent in productivity has become used instead of an evaporation method with low operating efficiency and high cost.
In a coating method, colloid particles with a low refractive index, such as magnesium fluoride, are effective as a micro-filler.
A water-based sol and an organosol, which is obtained by substituting the water-based sol with an organic solvent, are known as sols of colloid particles of magnesium fluoride (Patent Documents 1 and 2). However, since the surface of magnesium fluoride particles of these sols has high hydrophilicity, while a sol in which a disperse medium is a hydrophilic organic solvent such as alcohol can be produced as an organosol, a sol dispersed in a hydrophobic organic solvent cannot be produced.
Thus, a composition for a coating material obtained by mixture with a binder component or the like is limited to a binder component having a good compatibility with a hydrophilic organic solvent. Therefore, difficulty in producing a coating material composition using a hydrophobic organic solvent, has occurred.    [Patent Document 1]
Japanese Patent Application Publication No. JP-A-7-69621    [Patent Document 2]
Japanese Patent Application Publication No. JP-A-2-26824